Color stabilization of alkylarenesulfonic acids



nited St es Pate o REC? COLOR STABILIZATION or ALKYLARENE- SULFONICACIDS Leo J. Weaver, Creve 'Coeur, and Edwin J. Eccles, In,

Kirkwood, Mo., assignors to Monsanto Chemical Company, St. Louis,'Mo., acorporation of Delaware No Drawing. Application September 23, 1957Serial No. 685,422

6'Claims'. (cl. 260-505 J This invention relates to a process forproducing improved sulfonic acid compositions. More particularly, theinvention relates to a method for improving the color and colorstability of alkylarenesulfonic acids. A preferred embodiment of theinvention relates especially to such sulfonic acids obtained bysulfonation with liquid H SO or oleum.

remarkable benefits obtained therefrom, are illustratedAlkylarenesulfonate salts, and particularly long-chainalkylbenzenesulfonate salts, are outstanding surface-active agents foruse in synthetic detergent formulations, especially those adapted foruse as household detergents. Principally because of aestheticconsiderations it has recently become of considerable commercialimportance that alkylarenesulfonate salts should be as white aspossible. Unfortunately, however, the whiteness of alkylarenesulfonatesalts is limited by the color of the sulfonic acids. from which thesalts are preparedand. it is extremely difiicult to obtain the sulfonicacids free of darkly discoloring impurities.

In a copending application Serial No. 611,352, filed September 21, 1956,it has been disclosed that the color of alkylarenesulfonic acids can bemarkedly improved by a bleaching process utilizing hydrogen peroxide. Asis indicated in that application, the improved sulfonic acids producedby the bleaching process are not completely color stable-andconsequently must be converted to sulfonate salts soon after bleaching.If this were not done, the sulfonic acids would soon (within amatter ofa day or so) begin to redevelop the undesirable dark discoloration.

The. color instability of hydrogen peroxide bleached sulfonic acids isparticularly prevalent and noticeable in alkylarenesulfonic acidsproduced by sulfonation with liquid sulfuric acid and/or oleum.Consequently, a preferred embodiment of this invention is particularlyconcerned with such sulfonic acids. (Sulfonations with H 50 and witholeum are considered interchangeable for purposes of the presentinvention, and both are included in the term sulfuric acid sulfonation.)These latter sulfonic acids generally contain'free sulfuric aciddissolved or dispersed therein in considerably higher proportions (e.g.,more than about 3 wt. percent and as much as 15 or 20 wt. percent ormore) than the sulfonic acids prepared by S0 sulfonation.

We have now found that the color stability after bleaching theaforementioned alkylarenesulfonic acids can. be very much improved bytreating such sulfonic acids with alkaline neutralizing agents in minoramounts, and pref erably in an amount approximately sufiicient toconvert (on a stoichiometric basis) the free sulfuric acid in saidcomposition to a bisulfate salt.

The practice of the present invention, as well as the in the followingexample.

EXAMPLE A sample ofcrude dodecylbenzenesulfonic acid was 2 prepared bysulfonating dodecylbenzene (from benzene alkylation with propylenetetramer) with- 100% H SO' The crude dodecylbenezenesulfonic acid hadthe following analysis:

' Percent Dodecylbenzenesulfonic acid e 85.10 Sulfuric acid (as 100%)6.75 Unsulfonated oil 2.70 Water 5.45

Fifty parts by weight of the crude dodecylbenzenesulfonic acid wasdiluted with 5 parts by weight of water (in order to reduce theviscosity of the crude acid). Then, while holding the temperaturebetweenabout 45 and C., 1 part by weight of' 30% aqueous hydro genperoxide solution was added with mild agitation. The clarity of theresulting bleached composition was evaluated by determining the percenttransmission (relative to distilled water) of light through a 4% aqueoussolution. The determinations were made in a 50 millimeter rectangularcellutilizing aFisher electrophotometer equipped with a 425 millimicronblue filten flhelight transmission of the bleached acid was measuredimnediately after bleachingandat specified subsequent periodsduring-storage at 25 -2 6 C. The results are tabulated in the tablebelow.

A second sample ofthe crude dodecylbenzenesulfonic liater tedv Mar. 31

light transmission was then determined as with the preceding sample. 1 i

Table Relative Transmission Treatment First After 5 After 12 After 24After- Alter 82 Day, Days, Days, Days, Days, Days, Percent PercentPercent Percent Percent Percent mo, 7s 74 5s, 45 2s 1 10 HiO=+Na0H 88 8991 -89 91 81 From the foregoing results it is readily seen that sulfonicacid compositions bleached and treated according to the presentinvention are very markedly stabilized against color degradation.

It will be readily aparent to those skilled in the art that theprocedure described in the preceding example *first treated withhydrogen peroxide and then treated with an alkaline neutralizing agent.However, if desired or convenient this order of treatment can bereversed; or the two treatments can be carried out simultaneously. Inthe case of simultaneous treatment with hydrogen peroxide and. alkalineneutralizing agent, particular care should be. exercised in effectingsutliciently rapid removal of heat to maintain the reaction temperatur'ebelow'abo ut" 5'0 6655 0; If the temperature is allowedto rise above 50or 55 C; for more thana shorttime, there is a tendency towarddegradation and undesirable discoloration of the product.

It will be readily apparent that the present invention is applicable toa wide variety of alkylarenesulfonic acids. In general, it is applicableto long-chain alkyl substituted arenesulfonic acids such as those havingbetween about 9 and about 22 carbon; atoms in the alkyl groups. Theprocess is applicable to arenesulfonic acids, containing'a plurality ofalkyl groups, but treatment of monoalkylarenesulfonic acids ispreferred. Since the problems of discoloration are greater withalkylarenesulfonic acids in which thealkyl groups are branched(for-example, alkylarenesulfonic acids in which the alkyl group, isderived from polypropyleneor polybutylene) thepresent inventionisparticularly usefulin the treatment of branched-chain monoalkylarenesulfonic acids. I

The..amount of hydrogen peroxide to be utilized in" bleaching the crud esulfonic acid compositions .wlll depend to :a considerable extent uponthe "degree of discolora tionof the crude acid, thedesired degree ,ofbleaching,

the times and temperatures utilized in the bleaching step of theprocess, the efficiency with which the hydrogen peroxide isdispersed'within the crude acid, the form in which the hydrogen peroxideutilized'(for example, concentration of aqueous solution), etc.- Ingeneral, however, the amount of'hydrogen peroxideto be used will fallbetween about 0.1 wt. percent and-about 3 wt. percentyand preferablybetween about 0.5 wt. percent and about '2 wt. percent, based upon theweight of crude alkylar'enesulfonic acid.

Since one of the principal purposesof treating with an alkalineneutralizing agent is to atleast partially neutralize a substantialportionof the free sulfuric acid (though; without neutralizing'anappreciable proportion of' th e' sulfonic acid) it will'be readilyrecognized that a wide'variety of alkaline'neutralizing agents can beused in place of thesodium hydroxide of the foregoing example. Ingeneral, alkaline materials suchasthe alkali and alkaline earth metalhydroxides and carbonates (and particularly sodium, potassium or calciumhydroxides or carbonates) will be the most practical'neutralizingagents. However, ammonia, ammonium hydroxide, ammonium carbonate, andvarious organic amines such as mono, di, or triethanolamine, mono ordimethylamine, mono or diethylamine, cyclohexylamine ordicyclohexylamine, etc. can be used if desired.

. The amount .of alkaline. neutralizing agent used in the.

example described above was approximately sufiicient to convert. (onstoichiometric basis) thefree sulfuric acid to bisulfate ion, Thisconcentration can be varied somewhat'while still obtaining anappreciable degree of color stability. For example, concentrationsrunning as low as 40% (of the stoichiometric amount necessary to canvert H 80 to- HSO .)jwill.-still give' noticeablestabilizas tion. Theupper limit of concentration'is, considerably more criticalabout 120%being the upper operable limit for carrying out the process. v

. Some degree of care must be exercised with'respect to the amount ofwater which is allowed in the sulfonic acid compositions duringtreatment according to this invention. All crude compositions willcontain at least a small amount of water therein. As indicated above,further amounts of water may be added to reduce the viscosity of thecrude acid and facilitate further handling and treatment thereof.Moreover, since hydrogen peroxide and most alkaline neutralizing agentsare more readily handledas aqueous solutions, further quantities ofwater will often be introduced with these latter treating agents. If thetotal amount of water from all of these sources approaches theneighborhood of 30 wt. percent of the sulfonic acid compositions, thereis a strong tendency toward the formation of gel'structures which makefurtherhandling and treatme'utvery difficult; Consequently, it ispreferred that the total water concentration be-kept below about 25 wt.percent. When the ultimate sulfonic acid composition is to be utilizedin a so-called dry neutralization for the direct production of a dryfree-flowing detergent composition (as described in more detail in theearlier application Serial No. 611,352), it is preferred that the totalWater content be kept below about 10 wt. percent.

What is claimed is:

1. A process for producing a clear color-stabilized alkylarenesulfonicacid containing from about 9 to about 22 carbon atoms in the alkylgroups thereof, said stabilized alkylarenesulfonic acid being preparedfrom a crude alkylarenesulfonic acid having dispersed therein anappreciable proportion of sulfuric acid, which process comprisestreating said crude sulfonic acid with (1) hydrogen peroxide in a minoramount up to about 3 wt. per cent and (2) an alkaline neutralizing agentin a minor amount stoichiometrically sufficient-to convert a predominantproportion of the sulfuric acid to bissulfate salt without neutralizing.a substantial proportion of the sulfonic acid.

2. A process for producing a clear color-stabilized branched-chainalkylarenesulfonic acid containing from about 9 to about 22 carbon atomsin-the branched-chain alkyl group thereof, said stabilized sulfonic-acidbeing prepared from a crude branched-chain alkylarenesulfonic acidproducedby liquid phase-sulfuric acid sulfonation and containingdispersed therein anappreciable proportion greater than 1 wt. percent ofsulfuric acid, which process comprises treating said crude sulfonic acidwith (1) hydrogen peroxide in a minor amount up to about 3 Wt. percentand (2) an alkaline neutralizing agent in a minor amount up to about 1.2times that stoichiometrically sufficient to convert theaforesaid-sulfuric acid to a bisulfate salt.

3. A process for producing a clear color-stabilized branched-chainmonoalkylarenesulfonic acid containing from about 9 to about 22 carbonatoms in the alkyl group thereof, said stabilized sulfonic acid beingprepared from a crude branched-chain monoalkylarenesulfonic acidproduced by liquid phase sulfuric acid sulfonation and containingdispersed therein an appreciable proportion greater than 1 wt.percent'of sulfuric acid, which process comprises treating saidcrudesulfonic acid with (1) hydrogen peroxide'in a minor amount up toabout 3 wt. percent and (2) an alkaline neutralizing agent selected fromthe group consisting of alkali and alkaline earth metal hydroxides andcarbonates in a minor amount up to about 1.2 timesthat-stoichiometrically suflicient to convert the-aforesaidsulfuriczacid to a bisulfate salt.

4. A process for producing a clear color-stabilized branched-chainmonoalkylarenesulfonic. acid containing from .about'9 to 22. carbonatoms in. -the. alkyl group thereof; said-stabilized 'sulfonicacidbeing: prepared from.

a-crude. branched-chain monoalkylarenesulfonic acid produced by liquidphasev sulfuric 'acidIsulfonation and con-. taining.dispersed:thereinbetween about 1 and about 10 wt. percent of sulfuricacid, which process comprises treating said crude sulfonic acid with (1)hydrogen peroxide in a minor amount up to about 3 wt. percent and (2) analkaline neutralizing agent selected from the group consisting of alkalimetal and alkaline earth metal hydroxides and carbonates in a minoramount between about 40% and about %'of that stoichiometrically requiredto convert the aforesaid sulfuric acid to a bisulfate salt.

5. A process for producing a clear color-stabilized branched-chaindodecylbenzenesulfonic'acid, said stabilized sulfonic acid beingprepared from a crude branchedchain dodecylbenzenesulfonic acid producedby' liquid phase sulfuric acid sulfonation and containing dispersedtherein between about 1 and about 10 wt. percent of sufuric acid,which'process comprises treating said crude sulfuric acid, which processcomprises treating said crude sulfonic acid with (1) hydrogen peroxidein a minor amount between about 0.5 and about 2 wt. percent and (2)sodium hydroxide in an amount approximately stoichiometricallysufficient to convert the aforesaid sulfuric acid to a bisulfate salt.

References Cited in the file of this patent UNITED STATES PATENTS2,806,055 Feighner Sept. 10, 1957

1. A PROCESS FOR PRODUCING A CLEAR COLOR-STABILIZED ALKYLARENESULFONICACID CONTAINING FROM ABOUT 9 TO ABOUT 22 CARBON ATOMS IN THE ALKYLGROUPS THEREOF, SAID STABILIZED ALKYLARENESULFONIC ACID BEING PREPAREDFROM A CRUDE ALKYLARENESULFONIC ACID HAVING DISPERSED THEREIN ANAPPRECIABLE PROPORTION OF SULFURIC ACID, WHICH PROCESS COMPRISESTREATING SAID CRUDE SULFONIC ACID WITH (1) HYDROGEN PEROXIDE IN A MINORAMOUNT UP TO ABOUT 3 WT. PERCENT AND (2) AN ALKALINE NEUTRALIZING AGENTIN A MINOR AMOUNT STOICHIOMETRICALLY SUFFICIENT TO CONVERT A PREDOMINANTPROPORTION OF THE SULFURIC ACID TO BISSULFATE SALT WITHOUT NEUTRALIZINGA SUBSTANTIAL PROPORTION OF THE SULFONIC ACID.